A 4/8 would be even stronger. Almost no card at 6 mana has that powerful of a statline; I think it would be a solid legendary with a place in a lot of decks. It's hard to remove, trades super well (unlike its 7/5 counterpart, which is an unnecessarily aggressive statline) and generates constant value (especially for Jaina!). Sounds good to me!

That would make him better like you said, but all I want is Illidan to be good and if he was a 4/8 he would most likely be playable. But if Blizzard really wanted to push Illidan give him a new Battlecry. One example is Battlecry : destroy a demon , this is because Illidan is well A Demon Hunter ,this change could help with the current Warlock situation in the meta. If they wanted to make it more insane then make it so he destroys a minion. If Blizzard did this Illidan would become a very if not best 6 drop in the meta.

EDIT:Well I have to say that Illidian saved me from death, it's token is suprisingly strong (and they are elementals so they heal me) and you can earn his tokens for simply playing the game combo with Fire Fly easly gives you a big advantage.

So in the end Illidian found his home in my mage deck, card itself is powerful but it's kinda low hp might just turn you away from this card, but I think in the end it's worth it